What is the difference between a blood clot and a thrombus?

A clot is good when there is damage to the vascular tissue, but it is dangerous if it forms in a healthy blood vessel. In this case it is called a thrombus. Heparin, a drug active discovered one hundred years ago, is the anti-coagulant of choice most used to prevent and treat thrombosis, among other indications. Each year it saves more than 100 million lives.